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Estimating Weight of Gemstones

You cannot weigh a gem in a setting and it is rarely worth removing. Instead, you can get a close approximation of the weight by the gem’s volume.

In order to use these formulas, your measurements must be extremely accurate. Careful observation is also important. All these weights are adjusted by the stones proportions and it takes a trained eye to make those judgments.

 

Round faceted stones:
Diameter squared x depth x S.G. x .0018 = carat wt.

Oval faceted stones:
Length x width x depth x S.G. x .0020 = carat wt.

Emerald cut faceted stones:
Length x width x depth x S.G. x .0025 = carat wt.

Rectangular faceted stones:
Length x width x depth x S.G. x .0026 = carat wt.

Square cut faceted stones:
Length x width x depth x S.G. x .0023 = carat wt.

Marquise cut stones, (navette):
Length x width x depth x S.G. x .0016 = carat wt.

Pear cut stones:
Length x width x depth x S.G. x .0018 = carat wt.

Square cushions: (average corner meas.& belly meas. for diameter)
Diameter squared x depth x S.G. x .0018 = carat wt.

Rectangular Cushions: (average L & W for diameter)
Diameter squared x depth x S.G. x .0022 = carat wt.

Square step cut stones: (average both meas. for diameter)
Diameter squared x depth x S.G. x .0023 = carat wt.

Rectangular step cut stones:
Length x width x depth x S.G. x .0025 = carat wt.

Cabochon cut stones:
Length x width x depth x S.G. x .0027 = carat wt.